The present invention relates to a method and apparatus for substrate processing. More particularly, the present invention relates to an apparatus and a method for improved process gas distribution forming a variety of films including fluorosilicate glass (FSG) films.
One of the primary steps in the fabrication of modem semiconductor devices is the formation of a thin film on a semiconductor substrate by chemical reaction of gases. Such a deposition process is referred to as chemical vapor deposition (CVD). Conventional thermal CVD processes supply reactive gases to the substrate surface where heat-induced chemical reactions can take place to produce the desired film. Plasma enhanced CVD processes promote the excitation and/or dissociation of the reactant gases by the application of radio frequency (RF) energy to the reaction zone proximate the substrate surface thereby creating a plasma of highly reactive species. The high reactivity of the released species makes the process condition window for deposition larger than in thermal processes.
In one design of plasma CVD chambers, a vacuum chamber is generally defined by a planar substrate support, acting as a cathode, along the bottom, a planar anode along the top, a relatively short sidewall extending upwardly from the bottom, and a dielectric dome connecting the sidewall with the top. Inductive coils are mounted about the dome and are connected to a source radio frequency (SRF) generator. The anode and the cathode are typically coupled to bias radio frequency (BRF) generators. Energy applied from the SRF generator to the inductive coils forms a plasma within the chamber. Such a chamber is referred to as a high density plasma CVD (HDP-CVD) chamber.
In some HDP-CVD chambers and in other types of chambers, it is typical to mount two or more sets of equally spaced gas distributors, such as nozzles, to the sidewall such that the nozzles extend into the region above the edge of the substrate support surface. The gas nozzles for each set are coupled to a common manifold for that set; the manifolds provide the gas nozzles with process gases.
In one substrate processing chamber of this type, the nozzles have different lengths depending on the type of gas injected into the chamber through the nozzle. For example in this chamber, in some undoped silicate glass (USG) deposition processes using a process gas including silane (SiH4) and molecular oxygen (O2), precise amounts of silane are injected into the chamber with large amounts of oxygen so that enough oxygen exists to react with all the silane. Because so much oxygen exists, and often fills the chamber, it is commonly believed that the oxygen nozzle lengths do not affect the USG process significantly. In fact, for such a process, some chambers do not use nozzles at all to introduce oxygen but instead leak the oxygen into the chamber through holes in the chamber wall or walls.
In another type of substrate deposition chamber, it has been proposed to include multiple gas injection nozzles with some nozzles being on different levels from (e.g., above or below) other nozzles. It has also been proposed in these chambers that nozzles on higher levels extend further into the deposition chamber to aid in deposition uniformity.
In both the above described chambers and in other chambers, some gases may be injected together through common nozzles. Typically, gases that are injected together through common nozzles include gases that are not likely to react, or that react slowly enough during the delivery, with each other. For example, in deposition of the USG layer referred to above it is common to mix an inert gas such as helium or argon with either oxygen or silane prior to introducing those gases into the chamber.
Halogen-doped silicon oxide layers, and fluorine-doped silicate glass (FSG) layers in particular, are becoming increasingly popular in a variety of applications due to the low dielectric constants achievable for these films which are lower than the dielectric constants of USG films and their excellent gap-fill properties, especially for high speed semiconductor devices with increasingly smaller features sizes. In the deposition of FSG layers, it is common to use SiF4 as the fluorine source since SiF4 provides both Si and F species for fluorine-doped silicon oxide (SiOF). Other suitable gases include SiH2F2 and NF3. SiF4 can be introduced in the chamber separately from the other source gases, such as O2 and SiH4, but it would increase the complexity and cost of the system by requiring separate gas distribution apparatus. The need for additional gas injection nozzles inside the chamber would render the chamber less robust and make it more difficult to obtain process repeatability. Thus, it is common to mix the fluorine source with other gases that are chemically comparable (e.g., with the oxygen source) prior to introducing the gases into the chamber.
The fluorine source can also be mixed with a separate silicon source gas (e.g., SiH4, SiCl4, SiCH6, or SiC3H10) and injected from the same nozzle, but it will generate a relatively nonuniform film due to a more localized concentration of silicon source feeding. Fluorine is known to have a relatively long residence time. Thus, like oxygen, it is commonly believed that the length of the nozzle used to introduce a fluorine source into the chamber is not particularly important. It is commonly believed that the introduced fluorine will be distributed throughout the chamber because of its relatively long residence time.
Thus, for reasons discussed above, known deposition techniques currently used that employ separate silicon, oxygen and fluorine sources combine the fluorine source and oxygen source and flow the combination into the CVD chamber through relatively short nozzles while the separate silicon source (e.g., SiH4) is introduced (flowed) through longer nozzles. FSG films deposited in such a manner have physical properties acceptable for many applications. For some applications, however, improved deposition techniques are desirable.
The present invention is directed toward an improved substrate processing chamber having an improved process gas delivery system. The improved system is particularly applicable to the deposition of FSG films using SiF4 as a source of fluorine, but can also be used with many other processes. In part, the improvement is achieved by varying the length of the gas injection nozzles in a manner not previously known.
As described above, it was commonly thought that the length of the nozzles used to introduce a fluorine source into a substrate processing chamber for the formation of an FSG film was not particularly important because fluorine has a relatively long residence time in most chemical deposition chambers. The present inventors, however, discovered that this conventional thinking may result in the deposition of FSG layers having less than optimal properties in some instances. Specifically, the present inventors discovered that nozzle length affects the stability of FSG layers deposited from fluorine sources such as SiF4 in some processes. The inventors discovered that in addition to the uniform distribution of fluorine species across the substrate surface, that the uniform distribution of SiFx species (e.g., SiF, SiF2, SiF3) across the substrate surface helps create a stable FSG layer. When relatively short nozzles for the fluorine source are used, SiFx species are not distributed uniformly across the entire substrate surface. It is believed that the uneven distribution of SiFx species may result across the substrate surface. Thus, when SiFx species are formed near the orifices of the short nozzles, it is harder for the SiFx species to reach all areas of the wafer (e.g., the center). Instead, it is believed that the exhaust system pumps many of the SiFx species out of the chamber before they reach certain areas of the wafer, creating an uneven distribution of SiFx across the wafer with the center of the wafer receiving less SiFx than the perimeter.
In accordance with an embodiment of the invention, a method of forming a doped dielectric layer on a substrate surface in a process chamber includes injecting a first process gas containing precursor of a dielectric material into the process chamber at a first distance from a periphery of the substrate surface. A second process gas containing dopant species is injected into the process chamber at a second distance from the periphery of the substrate surface. The second process gas reacts with the first process gas in the process chamber to deposit a doped dielectric layer on the substrate surface. The second distance is substantially equal to or smaller than the first distance so as to distribute the dopant species substantially uniformly over the substrate surface to deposit a stable doped dielectric layer on the substrate and to better control the dopant level. In specific embodiments, the first distance ranges between about 1.75 and about 3.5 inches, and more preferably between about 2.75 and 3.25 inches; the second distance ranges between about 1.75 and about 3.5 inches, and more preferably between about 1.75 and 2.25 inches.
In accordance with another embodiment, an apparatus for forming a film on a substrate surface of a substrate disposed in a chamber defined by a housing includes a first plurality of nozzles extending into the chamber for introducing a first chemical containing precursor of a dielectric material at substantially a first distance from a periphery of the substrate surface. A second plurality of nozzles extend into the chamber for introducing a second chemical containing dopant species at substantially a second distance from the periphery of the substrate surface. The second distance is substantially equal to or smaller than the first distance. In some embodiments, the apparatus includes a removable ring having openings for receiving the first plurality of nozzles and second plurality of nozzles. In a specific embodiment, the housing includes a plurality of slots and a plurality of ring portions that are releasably inserted into the plurality of slots. The plurality of ring portions have openings for receiving the first plurality of nozzles and second plurality of nozzles.
In accordance with another embodiment of the invention, a method of forming a doped dielectric layer on a substrate surface in a process chamber includes injecting a first process gas containing precursor of a dielectric material into the process chamber at a first distance from a periphery of the substrate surface, and injecting a second process gas containing fluorine dopant species into the process chamber at a second distance from the periphery of the substrate surface. The second process gas reacts with the first process gas in the process chamber to deposit a dielectric layer containing fluorine on the substrate surface. The second distance is substantially equal to or smaller than the first distance.
In another embodiment of the present invention an apparatus is provided for use in a chemical vapor deposition system. In this embodiment, the deposition system includes a housing defining a chamber and a substrate support for supporting a substrate disposed within the chamber. The apparatus includes a gas ring having multiple openings disposed about an inner periphery of the ring. Some of the multiple openings couple to first nozzles that extend within the inner periphery to inject a first chemical into the chamber. Others of the multiple openings couple to second nozzles that extend within the inner periphery to inject a second chemical into the chamber. The distance that each of the first and second sets of multiple nozzles extend into the inner periphery is optimized and selected so that during use of the deposition system the desired first and second chemicals are substantially uniformly distributed across the substrate surface and so that reactant products (e.g., species) formed from the first and second chemicals that effect deposition uniformity are also uniformly distributed across the substrate surface with more uniform chemical properties. The present invention provides an apparatus that allows for uniform deposition of a variety of different film types within a single chamber without complicated hardware adjustments to the chamber.
These and other embodiments of the present invention, as well as some of its advantages and features are described in more detail in conjunction with the text below and attached figures.